#oneBlock .first {
  display: block;
  border: 1px solid black;
  background-color: grey;
}
#oneBlock .first:hover {
  background-color: white;
}
#header {
  width: 50%;
  width: calc(25vh - 20px);
  height: 10.5px;
  display: block;
  border: 1px solid black;
  background-color: grey;
  color: blue;
}
#header:hover {
  background-color: white;
}
